1. Field of the Invention
The present invention relates to a fuel injection device for an engine of a motorcycle in which a drive motor of an electronic control throttle body unit and a plurality of fuel injectors are arranged by utilizing a dead space formed between a fuel tank and an air cleaner.
2. Description of the Related Art
In general, in a motorcycle, an intake amount (volume) of an engine is controlled by a throttle body, and in a known art, the throttle body is controlled such that an accelerator operation and a throttle valve motion are operated in synchronism with each other by mechanically connecting an accelerator lever of a handle and a throttle valve.
However, in the motorcycle in which the accelerator grip of the handle and the throttle valve are mechanically connected together, the throttle valve is disadvantageously delayed in motion. Thus, it is difficult to improve discharge gas emission performance, safety or the like. In order to allow the throttle valve motion to quickly respond to the accelerator operation, an electronic control throttle body unit that electrically controls the throttle valve by a drive motor has been developed.
Meanwhile, some motorcycles include a fuel injection device as a device for supplying a fuel-air mixture to an engine of the motorcycle so as to respond to needs of engine characteristics and traveling performance. In such fuel injection device, sensors detect, as information, a throttle opening degree, an engine speed, an engine temperature, an outside air temperature, an atmospheric pressure or the like, and a computer (controller) processes the above information. The fuel injection device thereby directly injects a most appropriate required amount of fuel to an intake passage of the engine by using a fuel injector. Fuel efficiency and engine power can be improved. Since only the minimum required amount of fuel is injected, a fuel injection amount can be also decreased.
The electronic control throttle body unit is provided for the fuel injection device for the engine of the motorcycle in some cases as described in Patent Documents 1 and 2 (Japanese Patent Laid-Open Publication Nos. 2002-256896 and 2002-256895). The electronic control throttle body unit electrically controls the throttle valve by using an electronic control throttle drive motor operated in association with the accelerator lever. In the electronic control throttle body unit, arrangement of the drive motor and the fuel injector is considered to be important in order to achieve reductions in vehicle size and weight as well as favorable fuel performance.
When the engine speed varies largely and frequently as in the motorcycle, only one fuel injector may not sufficiently supply fuel in an amount required for the operation of the engine. Thus, a plurality of fuel injectors are arranged in the throttle body so as to constitute an intake passage, or in the vicinity thereof in some cases so as to supply a sufficient amount of fuel (Patent Documents 3 or 4 (Japanese Patent Laid-Open Publication Nos. 2009-103137 and 2005-16391)).
The Patent Document 1 discloses a drive motor arranged between a cylinder head and an air cleaner in an engine of a motorcycle, and hence, a filter of the air cleaner has a smaller size, so that filter purification performance is be deteriorated. In addition, since a fuel injector is arranged in a throttle body, fuel is injected from a position apart from an intake valve of the engine, and an engine speed response to a throttle valve operation is thereby lowered, thus being disadvantageous.
The Patent Document 2 discloses a fuel injector and a drive motor arranged on the same side surface of a throttle body. Thus, a throttle valve is arranged apart from an intake valve of an engine, and accordingly, an engine speed response to a throttle valve operation is also lowered, thus being disadvantageous.
Both the inventions described in the Patent Documents 1 and 2 do not include two fuel injectors.
On the other hand, the Patent Documents 3 and 4 disclose a second fuel injector that is arranged within an air cleaner above an air funnel. According to such arrangement, although capacity of the air cleaner is decreased, the second fuel injector blocks a flow of intake air, thereby possibly deteriorating an intake inertia effect and reducing (decreasing) engine power. Moreover, since the second fuel injector injects the fuel within the air cleaner, a lot of spray is scattered in the air cleaner due to spitback from the engine or a disturbance of the intake air. Thus, an inner portion of the air cleaner is contaminated, or much fuel is adhered thereto, resulting in a deterioration of fuel consumption and thus, being disadvantageous.